JPS60131170A - Screwing device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a screw tightening device using an electric motor as a driving source.

Conventional configuration and its problems An example of the configuration of a conventional screw tightening device is shown in FIG.

1 is a driving electric motor, 2 is a motor shaft, and 3 is a speed reducer using a planetary gear mechanism. 4 is a gear fixed to the motor shaft 2, 5 is a planetary gear, 6 is an internal gear, 7 is a gear support plate that rotates with the revolution of the planetary gear 5, and 8 is fitted into a screw hole in a screw head. This is the bit part that matches.

9 is a bearing that rotatably supports the bit, 1O is a cover for a screw tightening device, and the outer cover is a grip portion.

Furthermore, 11 is a current cutoff circuit that cuts off the motor current iM of the electric motor 1, and 12 is a power cord connected to a power source.

Here, the operation of the screw tightening device during screw tightening will be explained with reference to FIG. 2. Figure 2 shows the motor current iM and the motor rotation speed n from the start to the end of the screw tightening operation.
This figure shows the changes in time t. When a power switch (not shown) is turned on, a starting current flows through the motor 1, and the motor 1 starts rotating. After reaching the starting peak current ip, the motor current iM decreases as the rotation speed of the motor 1 increases, and reaches the maximum rotation speed n1 and the minimum current i1 at time t1. The period from time t1 to time t12 is an idle tightening period of the screw until the screw head contacts the workpiece. Then, at time t2, the screw head sinks into the workpiece, and tightening of the screw is started.

As the screw tightens, the rotation speed n of the electric motor 1 begins to decrease.
Accordingly, the motor current iM begins to rise. Here, the current cutoff circuit 11 has a current detection circuit that compares the detected current value detected by the current detection circuit when tightening the screw with a preset set current value, and that the detected current value is higher than the set current value. It has a built-in circuit that cuts off the motor current iM when it becomes larger than the current value. (The current cutoff circuit can be easily configured using transistors, OP amplifiers, digital ICs, etc., and its specific configuration is not directly related to the explanation of the present invention, so the explanation will be omitted.) When the set current value of the current cutoff circuit is set to 13, the time t
At , the motor current 1M is cut off and becomes zero.

What is important here is that the rotation of the motor is not zero at time t3. Therefore, at time t3, inertial energy is stored in each of the motor rotor, gear 4, planetary gear 5, gear support plate 7, and bit part 8, and this energy is used to tighten the screw between time t3 and time 141. It appears as energy. Generally t
The time from t4 to t4 is very short (about several m3), so when tightening a screw using inertial energy, the torque becomes a very large value. Therefore, the shock to the worker between time t3 and time t4 is very large, and since the magnitude of the tightening torque is also determined mostly by the magnitude of inertial energy, tightening can be done by changing the set current value. It has the disadvantage that even if you try to make it variable, it cannot be done.

OBJECTS OF THE INVENTION The present invention was made in view of the above-mentioned drawbacks, and it is an object of the present invention to provide a screw tightening device that prevents inertial energy from being transmitted to the bit portion, produces less shock, and has good tightening accuracy.

Composition of the Invention The present invention provides an electric motor that serves as a driving source for screw tightening rotational force, a planetary gear mechanism that reduces the rotation speed of the electric motor, and an internal gear of the planetary gear mechanism that is rotated by the rotation of the shaft of the electric motor. It consists of a bearing that supports the internal gear freely and a means for preventing rotation of the internal gear and fixing it to the case.By allowing the internal gear to rotate freely when the screw is tightened, the inertia energy of the motor rotor and the gear is reduced. The screw tightening operation is performed without transmitting the torque to the bit part.

DESCRIPTION OF EMBODIMENTS The present invention will be described below with reference to FIG. 3, which shows one embodiment thereof. 1, 2, 4.5, and 7 to 12 are the same components as in the conventional example shown in FIG. 1, so their explanations will be omitted. 1
Reference numeral 3 denotes an internal gear that is not fixed to the force and is rotatable around the shaft 2 of the electric motor 1, and has a plurality of holes 14 on the thrust end surface. 15 is a bearing that allows the internal gear to rotate freely around the shaft 20 of the electric motor. Numeral 17 is a solenoid having a moon (-16) that fits into the hole 14 provided in the thrust end face of the internal gear 13, and is fixed to the cover 1○. When the internal gear 13 is attracted and disengaged from the hole 14 of the internal gear 13, and the internal gear 13 becomes freely rotatable, and the solenoid 17 is not energized, the mover 16 moves through the plurality of holes provided in the internal gear 13. It has a structure that fits into one of the 14.

The operation of the apparatus having the above configuration will be explained based on FIG. 4. At 13 years from time t0, the solenoid 17 is not energized, the mover 16 is fitted into the hole 14 of the internal gear 13, and the internal gear 13 is fixed to the case 1o. In this case, the screw tightening device is exactly the same as the conventional example shown in FIG.
3, the operation is exactly the same as that of the conventional example shown in FIG.

At time t3, when the motor current iM of the motor 1 reaches a preset value i3, the current cutoff circuit 11 is activated and the motor current iH becomes zero. At this time, the solenoid 17 is energized, the mover 16 is disengaged from the hole 14 provided in the internal gear 13, and the internal gear 13 is made rotatable. In this case, the rotation speed of the electric motor 1 is n3, and the electric motor rotor and each gear store inertial energy, but the internal gear 1
3 is rotatable with respect to the cover 10, the inertial energy is used as energy to turn the internal gear.
Therefore, no torque is transmitted to the bit portion 8 due to the tightening due to inertial energy.

In the above description, the mover 16 of the solenoid 17 and the plurality of holes 14 provided in the internal gear 13 were used as means for fixing the internal gear 13 to the case 10 or making it rotatable. It is obvious that it can be constructed with a ratchet mechanism driven by.

Effects of the Invention As is clear from the above embodiments, the screw tightening device of the present invention is configured so that the inertial energy of the rotor of the electric motor and the reduction gear is not transmitted to the bit when tightening the screw. Tightening has the unique effect of being able to accurately control the torque by controlling the motor current, and minimizing the shock to the operator when tightening screws, and this effect is extremely impressive. .

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a conventional screw tightening device, Fig. 2 is an explanatory diagram of the operation of the same screw tightening device, Fig. 3 is a sectional view of a screw tightening device showing an embodiment of the present invention, and Fig. 4 is a sectional view of a conventional screw tightening device. It is an explanatory view of operation of the same screw tightening device. 1... Electric motor, 6... Planetary gear, 13... Internal gear, 14... Hole, 15... Bearing, 16...
...mover (means to prevent rotation or allow rotation)
, 17... Solenoid. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 COc+ r2 C3D# lI'f threshold Figure 3

Claims (1)

[Claims] an electric motor that serves as a drive source for screw tightening rotational force; a planetary gear mechanism that reduces the rotational speed of the electric motor; a bearing that rotatably supports an internal gear of the planetary gear mechanism around a shaft of the electric motor; A screw tightening device equipped with a means for preventing or allowing rotation of an internal gear.